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IMPROVEMENTS IN THE LA-72, LA-22 and LA-12

COMPARED TO LA-70B, LA-135, LA-200

1. RF Power output metering is optionally available, including peak reading on forward power.

  • The LA-x2 Amplifiers do not need an external watt meter for tune up.
  • Peak Reading function allows tune up with strings of dits or dahs instead of a key down which carrier which is less stressful on RF relays, connectors and cables.
  • Peak power function allows accurate monitoring of SSB voice and CW Morse Code power output.
  • Power meter is calibrated at each amateur band giving better accuracy than wide range elements.

2. Reflected RF power metering is optionally available.

  • Can check antenna / feed lines for problems without an external power or SWR meter.

3. GND to TX switching circuit has a 14VDC max.. open circuit voltage (was 28 VDC).

  • Directly compatible with multimode VHF transceivers that typically have a 20 VDC max. voltage open collector switching transistors.

4. 28 VDC control supply is regulated.

  • Meter lamps don't dim on TX,
  • More tolerant to line voltage variations
  • Relay switching voltage more stable under high loads.
  • Cathode warm up time delay is more consistent.

5. Both Heater & Control transformers are VDE certified (IEC 950. VDE 0805)

  • Higher primary isolation, less affected by AC power feed noise.
  • European regulatory compliance.

6. Control transformer is a 43 VA unit instead of 30 VA.

  • 700 ma. continuous relay output current available, (old was 400 ma. CCS ).
  • Now able to handle more types and varieties of relays.

7. The HV meter resistor string has a 4.2 KV working voltage rating vs.. 3600V in the older models (3000V in early LA-70B models) and metal film resistors are used in place of carbon film resistors.

  • Improved HV meter accuracy.
  • Less HV meter drift, with temperature change and aging.

8. Q5 & Q7, TX switching transistors now 3A units.

  • Able to handle higher relay loads with less chance of failure.
  • Have lower forward voltage drop, better voltage to external RF relays.
  • Less heat.
  • Less chance for failure.

9. Built in switching for running multiple LA-amplfiers from a single PS-70

  • no longer have to build add on circuitry.

10. HV , GRID and PLATE meter calibration potentiometers added.

  • Can more accurately calibrate meters,
  • No longer have to unsolder and replace resistors to re-calibrate meters.

11. Time delay adjustment potentiometer added.

  • Can set time delay to exactly 3:00 min.
  • Time delay is now easily adjustable without having to unsolder a resistor.

12. New Plate & HV meters are more linear and faster responding.

  • Readings are more accurate over their entire range.

13. Load Capacitor is made from spring temper phosphor bronze.

  • Allows greater load adjustment range
  • Won't develop a permanent bend which limits maximum loading.

14. Black color power coated wrap around top cover optionally availble.

  • Cover is more resistant to scratches than old irridite finish.
  • Improved appearance.
  • Old style gold iridite top cover is still available (standard) to match existing LA-70B, LA-135 and LA-200 amplifiers.

15. Front panel is epoxy powder coat in place of anodize finish.

  • Front panel appearance and color is more constant among amplifiers from different production batches.
  • Front panel lettering is now sharper and more consistent for better appearance and legibility.
  • Power coat finish is very resistant to scratching.

16. LA-72 has a RF output Low Pass filter standard (was optional in the LA-70B).

  • Spurious emissions are now down more than -60 dBc.
  • 3rd harmonic (1296 MHz) is typically down >70 dB, which is important for multi-operator contest operation.

17. The LA-72 uses a 1/4 wv. shorted stub on the RF output in place of a RF choke.

  • The 2nd harmonic is reduced substantially below -60 dBc.
  • Stray coupling to the old RF choke is eliminated, substantially reducing the strength of the 5th and higher harmonics.

18. The Cathode Tune capacitor has wider spaced plates giving it a higher voltage rating.

  • Greatly reduces the possibility of arcing the Cathode Tune capacitor if the LA-x2 amplifier is accidentally over driven or mis-tuned.

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